Apparatus and method for diagnosing deterioration of catalyst, and catalytic converter apparatus for exhaust emission of engine

ABSTRACT

An apparatus for diagnosing deterioration of a catalyst for an internal combustion engine, having a first catalyst and a second catalyst and provided with sensors for detecting a particular exhaust component before and after the first catalyst, wherein a relationship between a deterioration property involved in clarification of an exhaust gas of the internal combustion engine by a combination of the first catalyst and the second catalyst and a deterioration property of the first catalyst are determined previously; a deterioration degree of the first catalyst is calculated according to outputs from the sensors disposed before and after the first catalyst; deterioration of the first catalyst is judged according to the deterioration degree; and deterioration of the second catalyst is judged according to the deterioration degree of the first catalyst.

BACKGROUND OF THE INVENTION

The present invention relates to an apparatus and method for diagnosingdeterioration of a catalyst for an internal combustion engine (called anengine for short) and a catalytic converter apparatus for exhaustemission of the engine, and more particularly to an apparatus and methodfor diagnosing deterioration of a catalyst to judge deterioration of athree-way catalyst for purification of exhaust gas disposed in anexhaust gas passage of the engine and a catalytic converter apparatusfor exhaust emission of the engine.

Deterioration of a catalyst for an engine having a plurality ofcatalysts for purification of exhaust gas disposed in an exhaust pipe isdiagnosed by oxygen sensors disposed before and after the catalyst whichis located closest to the engine exhaust port and according to outputsfrom the two oxygen sensors. Where it is judged according to the outputsfrom the oxygen sensors that the subject catalyst is ineffective (lostof exhaust emissions reduction capability), all the plural catalysts arereplaced.

There is another prior art related to a diagnostic apparatus in that afront catalyst (upper stream catalyst) and a rear catalyst (down streamcatalyst) are disposed in an exhaust gas passage, oxygen sensors eachare mounted on the upper stream of the front catalyst, the intermediatesection between the front and rear catalysts and the down stream of therear catalyst, the front catalyst is diagnosed by the oxygen sensorsmounted on the upper and lower streams of the front catalyst, and thefront catalyst and the rear catalyst are collectively diagnosed by theoxygen sensor on the upper stream of the front catalyst and the oxygensensor on the down stream of the rear catalyst (e.g., U.S. Pat. Nos.5,740,676 and 6,003,309).

SUMMARY OF THE INVENTION

The emission control regulation is being tightened every year, and athreshold value level of deterioration judging for judging a catalyst asineffective is becoming low accordingly, so that it is necessary to makejudgment of effective/ineffective when the catalyst is slightlydeteriorated.

But, the prior art cannot detect accurately a slight degree ofdeterioration of the catalyst. Therefore, it becomes difficult todiagnose accurately the deterioration of the catalyst in compliance withthe emission control regulation which is tightened more and more everyyear.

In a case where the deterioration is diagnosed by a conventionalcatalyst system having a plurality of catalysts disposed in an exhaustpipe, an effective rear catalyst is also replaced when a front catalystis judged as ineffective, so that the catalyst replacement cost becomeshigh. And, even if the oxygen sensor is disposed before and after theindividual catalysts, the system cost increases.

The present invention has been made in view of the above circumstancesand provides an apparatus and method for diagnosing deterioration of acatalyst that can perform an accurate diagnosis of the deterioration ofthe catalyst and a catalytic converter apparatus for exhaust emission incompliance with the emission control regulation being tightened more andmore every year and can reduce the cost.

In order to complete the object, the apparatus for diagnosingdeterioration of a catalyst for an internal combustion engine accordingto the present invention is an apparatus for diagnosing deterioration ofa catalyst for an internal combustion engine, having a first catalystand a second catalyst and provided with sensors for detecting aparticular exhaust component before and after the first catalyst,wherein a relationship between a deterioration property involved inclarification of an exhaust gas of the internal combustion engine by acombination of the first catalyst and the second catalyst and adeterioration property of the first catalyst are determined previously;a deterioration degree of the first catalyst is calculated according tooutputs from the sensors disposed before and after the first catalyst;deterioration of the first catalyst is judged according to thedeterioration degree; and deterioration of the second catalyst is judgedaccording to the deterioration degree of the first catalyst.

The apparatus for diagnosing deterioration of a catalyst for an internalcombustion engine according to the invention preferably adds a volume ofa space between the first catalyst and the second catalyst to elementscontributing to the deterioration of the second catalyst when arelationship of the first catalyst to the deterioration property due tothe combination of the first catalyst and the second catalyst isderived.

In the apparatus for diagnosing deterioration of a catalyst for aninternal combustion engine according to the invention, the sensors fordetecting the particular exhaust component are O₂ sensors which output abinary output for the presence or not of oxygen contained in the exhaustgas or sensors which output a signal corresponding to an oxygen densityor a fuel concentration contained in the exhaust gas.

In order to achieve the object, the method for diagnosing deteriorationof a catalyst for an internal combustion engine according to theinvention is a method for diagnosing deterioration of a catalyst for aninternal combustion engine, having a first catalyst and a secondcatalyst and provided with sensors for detecting a particular exhaustcomponent before and after the first catalyst, comprising determiningpreviously a relationship between a deterioration property involved inclarification of an exhaust gas from the internal combustion engine by acombination of the first catalyst and the second catalyst and adeterioration property of the first catalyst; calculating adeterioration degree of the first catalyst according to outputs from thesensors disposed before and after the first catalyst; judgingdeterioration of the first catalyst according to the deteriorationdegree; and judging deterioration of the second catalyst according tothe deterioration degree of the first catalyst.

In order to achieve the object, the catalytic converter apparatusaccording to the invention is a catalytic converter apparatus forexhaust emission which is disposed in an exhaust gas passage of aninternal combustion engine, the apparatus being separated into a firstcatalyst and a second catalyst, and a volume of the first catalystdisposed on the upper stream side of an exhaust gas flow in the exhaustgas passage is smaller than that of the second catalyst.

The catalytic converter apparatus according to the invention preferablyhas a proportion of a volume of the first catalyst to that of the secondcatalyst determined to be smaller according to a proportion of anunburnt gas conversion efficiency of a combination of the first andsecond catalysts when they are new to an unburnt gas conversionefficiency at the time when an emission level is judged as failure.

The catalytic converter apparatus according to the invention preferablyhas the first catalyst and the second catalyst stored in one and thesame housing.

It is known that the catalyst is deteriorated starting from its frontportion which is closer to the exhaust port of the internal combustionengine. Accordingly, the present invention divides the catalystaccording to a proportion between an unburnt gas conversion efficiencyat the time of a combination of new catalysts and an unburnt gasconversion efficiency when an emission level is judged as failure, sothat even if the deterioration is little as a whole, the front catalystprovided with an oxygen sensor is deteriorated quickly, and it is easyto detect a deterioration degree. The deterioration of the rear catalystis determined according to the deterioration degree and the number ofreplacement times of the front catalyst, so that the front catalyst isnot replaced even if it is deteriorated.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall structure view showing one embodiment of a controlsystem of an internal combustion engine (engine) to which the apparatusfor diagnosing deterioration of a catalyst according to the invention isapplied.

FIG. 2 is a block diagram showing one embodiment of an internalcombustion engine control unit to which the apparatus for diagnosingdeterioration of a catalyst according to the invention is applied.

FIG. 3 is a control block diagram of an engine control unit forperforming a method for diagnosing deterioration of a catalyst accordingto the invention.

FIG. 4 is a block diagram showing one embodiment of a front catalystdeterioration degree arithmetic processing section which is included ina catalyst deterioration detection unit for performing the method fordiagnosing deterioration of a catalyst according to the invention.

FIG. 5 is a graph showing an example of a relationship between acorrelation value and a deterioration degree of the outputs of the frontand rear O₂ sensors.

FIG. 6A, FIG. 6B, FIG. 6C are a structure view of a general example of acatalytic converter apparatus not according to the present invention andgraphs showing examples of behaviors of the outputs of the front andrear O₂ sensors when it must be judged as catalyst ineffective.

FIG. 7A, FIG. 7B, FIG. 7C are a structure view of the catalyticconverter apparatus according to the invention and graphs showingbehaviors of the outputs of the front and rear O₂ sensors when it mustbe judged as catalyst ineffective, and FIG. 7D is a graph showing acomparative example of the output of the rear O₂ sensor.

FIG. 8 is a graph showing an example of a relationship between acorrelation value and a deterioration degree of the outputs of the frontand rear O₂ sensors of the catalytic converter apparatus according tothe invention.

FIG. 9 is a graph showing an example of a relationship between a frontcatalyst deterioration degree and a rear catalyst deterioration degreeof the catalytic converter apparatus according to the invention.

FIG. 10 is a graph showing an example of a relationship between a frontcatalyst deterioration degree and a front catalyst deterioration degreeintegrated value (rear catalyst deterioration index) of an apparatus fordiagnosing deterioration of a catalyst according to the invention.

FIG. 11 is an explanatory view showing a catalyst separation example ofthe catalytic converter apparatus according to the invention.

FIG. 12 is a block diagram showing an example of one structure of aneffective/ineffective judgment processing section for the front catalystand the rear catalyst of the apparatus for diagnosing deterioration of acatalyst according to the invention.

FIG. 13 is a block diagram showing an example of another structure ofthe effective/ineffective judgment processing section for the frontcatalyst and the rear catalyst of the apparatus for diagnosingdeterioration of a catalyst according to the invention.

FIG. 14 is a block diagram showing in detail the rear catalysteffective/ineffective judging section of the apparatus for diagnosingdeterioration of a catalyst according to the invention.

FIG. 15 is a flowchart showing a processing flow of overall controlperformed by an engine control unit including catalyst deteriorationjudgment of the embodiment.

FIG. 16 is a flowchart showing a processing flow for calculation of acatalyst deterioration degree of the front catalyst by a front catalystdeterioration degree arithmetic processing section of the embodiment.

FIG. 17 is a flowchart showing a processing flow for judgment ofeffective/ineffective of the front catalyst and the rear catalystperformed by an effective/ineffective judgment processing section of theembodiment.

FIG. 18 is a flowchart showing a processing flow of the front catalystdeterioration judging value integration and the judging value storingperformed by an ineffective judgment processing section.

FIG. 19 is a flowchart showing a processing flow for judgment ofeffective/ineffective of the front catalyst and the rear catalystperformed by the effective/ineffective judgment processing section ofanother embodiment.

FIG. 20 is a flowchart showing a processing flow for judgment ofeffective/ineffective of the rear catalyst performed by the rearcatalyst effective/ineffective judging section of the embodiment.

FIG. 21 is an overall structure view showing another embodiment of theinternal combustion engine (engine) to which the apparatus fordiagnosing deterioration of a catalyst of the invention is applied. Itis another example of the engine and its periphery controlled by thefuel control device of the invention.

DESCRIPTION OF THE EMBODIMENTS

One embodiment of an internal combustion engine (called an engine forshort) to which the apparatus for diagnosing deterioration of a catalystaccording to the invention is applied will be described with referenceto FIG. 1.

An engine 201 has in an intake system a throttle valve 202 which is ametering device for an amount of intake air, an idle speed control valve(ISC valve) 203 which controls the idling speed of the engine 201 bycontrolling a passage area of a passage which bypasses the throttlevalve 202 and is connected to an intake pipe 204, an intake pipepressure sensor 205 which detects a pressure within the intake pipe 204,and fuel injection valves 206 which inject fuel required by the engine201.

The engine 201 is provided with ignition plugs 208 for igniting amixture of air and fuel supplied into cylinders (combustion chambers)207, and ignition coils (ignition modules) 209 for supplying an ignitionenergy to the ignition plugs 208 according to the ignition signal beingoutputted from an engine control unit 250.

The engine 201 is also provided with a cam angle sensor 210 fordetecting a cam angle and a water temperature sensor 211 for detecting atemperature of cooling water.

An exhaust pipe 221 has a front catalyst (upper stream catalyst=firstcatalyst) 223 as a three-way catalyst and a rear catalyst (down streamcatalyst=second catalyst) 224 as a three-way catalyst which areseparately disposed within a single housing 222.

Specifically, the catalytic converter apparatus for exhaust emission isdivided into the front catalyst 223 and the rear catalyst 224, and thefront catalyst (the upper stream catalyst) 223 which is mounted on theupstream side of the rear catalyst 224 viewed from an exhaust gas flowthrough the exhaust pipe 221 has a volume smaller than that of the rearcatalyst (the down stream catalyst) 224. And, an intermediate space 225is defined between the front catalyst 223 and the rear catalyst 224within the housing 222.

A front O₂ sensor 226 which detects an oxygen density in exhaust gas andoutputs a binary signal is mounted on the upper stream side (viewed fromthe exhaust gas flow in the exhaust pipe 221) of the front catalyst 223of the exhaust pipe 221. The housing 222 is provided with a rear O₂sensor 227 which detects an oxygen density in the exhaust gas within theintermediate space 225 and outputs a binary signal.

The engine 201 is operated and stopped by an ignition key switch 212which is a main switch.

The idling speed of the engine 201 in this embodiment is controlled bythe idle speed control valve 203, but where the throttle valve 202 iscontrolled by means of a motor or the like, the idling speed can becontrolled by the throttle valve 202, and the idle speed control valve203 can be eliminated.

Fuel control including air/fuel ratio control of the engine 201,ignition timing control, idle control and catalyst deteriorationdiagnosis are performed by the engine control unit 250.

The engine control unit 250 is, for example, anelectronically-controlled type based on a microcomputer and as shown inFIG. 2, comprised of an I/O LSI (Input/Output Large-scale integratedcircuit) 251 which converts electrical signals of the individual sensorswhich are mounted on the engine 201 into signals for digital arithmeticprocessing and converts the control signals for digital calculation intodrive signals for a real actuator, an arithmetic unit (MPU) 252 whichjudges the state of the engine 201 according to the signals for digitalarithmetic processing from the I/O LSI 251, performs arithmeticprocessing of an amount of fuel, ignition timing, catalyst deteriorationdiagnosis and the like required by the engine 201 according to aprescribed procedure and sends the calculated values to the I/O LSI 251,a nonvolatile memory (EP-ROM) 253 which stores the control procedure andcontrol constant of the arithmetic unit 252, and a volatile memory (RAM)254 which stores the results calculated by the arithmetic unit 252.

Even if the ignition switch 212 is off and power is not supplied to theengine control unit 250 from a battery power supply, a back-up powersupply may be connected to the volatile memory 254 in order to store thememory contents.

In this embodiment, the engine control unit 250 receives signals fromeach of the water temperature sensor 211, the cam angle sensor 210, acrank angle sensor 213, the front O₂ sensor 226, the rear O₂ sensor 227,the intake pipe pressure sensor 205, a throttle opening degree sensor214 and the ignition switch 212, and outputs a fuel injection commandsignal to the fuel injection valves 206, an ignition command signal tothe ignition coils 209 and an opening degree command signal to the idlespeed control valve 203, and a display command to a failure diagnosisdisplay unit 261 according to a catalyst deterioration diagnosed result.

Then, one embodiment of a control block of the engine control unit 250to perform a method for diagnosing deterioration of a catalyst accordingto the invention will be described with reference to FIG. 3.

The engine control unit 250 executes a computer program to embody anengine speed calculation unit 101, a basic fuel calculation unit 102, abasic fuel correction factor calculation unit 103, a basic ignitiontiming calculation unit 104, an ISC control unit 105, an accelerationand deceleration judging unit 106, an air/fuel ratio feedback controlcoefficient calculation unit 107, a catalyst deterioration detectionunit (catalyst deterioration diagnostic unit) 108, a basic fuelcorrection unit 109, and an ignition timing correction unit 110 by meansof software.

The engine speed calculation unit 101 counts the electrical signals ofthe crank angle sensor 213 which is set to a prescribed crank angleposition of the engine 201, mainly the number of inputs per unit time ofchanges in pulse signals, and calculates the number of revolutions perunit time of the engine 201 by performing arithmetic processing.

The basic fuel calculation unit 102 calculates basic fuel which isrequired by the engine 201 according to the engine speed calculated bythe engine speed calculation unit 101 and an intake pipe pressure(engine load) detected by the intake pipe pressure sensor 205 which ismounted on the intake pipe 204 of the engine 201.

The basic fuel correction factor calculation unit 103 calculates acorrection factor of the basic fuel, which is calculated by the basicfuel calculation unit 102, in the individual operation regions of theengine 201 according to the engine speed calculated by the engine speedcalculation unit 101 and the intake pipe pressure (engine load) detectedby the intake pipe pressure sensor 205.

The basic ignition timing calculation unit 104 determines optimumignition timing of the engine 201 by map retrieving or the like based onthe engine speed calculated by the engine speed calculation unit 101 andthe intake pipe pressure(representing engine load) detected by theintake pipe pressure sensor 205.

The ISC control unit 105 determines a target idling speed value in orderto keep the idling speed of the engine 201 at a prescribed value andcalculates a target flow rate and an ISC ignition timing compensationamount to the ISC valve 203. The ISC control unit 105 outputs an ISCvalve signal based on the target flow rate to the ISC valve 203. Thus,the ISC valve 203 is driven so as to provide the target flow rate foridling.

The acceleration and deceleration judging unit 106 processes electricalsignals outputted from the throttle opening degree sensor 214 to judgefrom the throttle opening degree change amount whether the engine 201 isin an acceleration or deceleration state and calculates an ignitiontiming compensation amount for the acceleration or deceleration.

The air/fuel ratio feedback control coefficient calculation unit 107performs air/fuel ratio feedback control according to a sensor signal ofthe front O₂ sensor 226 on the upper stream side of the front catalyst223, an engine speed, an intake pipe pressure and an engine watertemperature.

The catalyst deterioration detection unit 108 judges a deteriorationdegree of the front catalyst 223 according to the sensor signal of thefront O₂ sensor 226 which is on the upper stream side of the frontcatalyst 223, the sensor signal of the rear O₂ sensor 227 which is onthe down stream side of the front catalyst 223, the engine speed, theintake pipe pressure and the engine water temperature and also judges adeterioration degree of the rear catalyst 224 according to the judgedresult. The catalyst deterioration detection unit 108 outputs a displaycommand to the failure diagnosis display unit 261 to notify a driverabout a catalyst failure according to the ineffective/effective judgmentmade on the basis of the deterioration degree.

The basic fuel correction unit 109 corrects the basic fuel, which iscalculated by the basic fuel calculation unit 102, by using thecorrection factor of the basic fuel correction factor calculation unit103, the air/fuel ratio feedback control coefficient of the air/fuelratio feedback control coefficient calculation unit 107 and the like andoutputs the fuel injection command signal according to the correctedamount of fuel to the fuel injection valves 206 of the individualcylinders. Thus, the fuel injection valves 206 inject a required amountof fuel into the individual cylinders.

The ignition timing correction unit 110 corrects the basic ignitiontiming, which is determined by the basic ignition timing calculationunit 104, by using the ISC ignition timing compensation amount of theISC control unit 105, the ignition timing compensation amount foracceleration or deceleration of the acceleration and decelerationjudging unit 106 and the like and outputs the corrected ignition timingcommand signal to the ignition coils 209 of the individual cylinders.Thus, the ignition plugs 208 of the individual cylinders cause a sparkdischarge with the required ignition timing to ignite the mixtureflowing into the cylinders.

In this embodiment, the fuel control is established by detecting anintake pipe pressure, but the fuel control can also be established bydetecting an amount of intake air of the engine 201.

One embodiment of the front catalyst deterioration degree arithmeticprocessing section included in the catalyst deterioration detection unit108 will be described in detail with reference to FIG. 4.

The catalyst deterioration detection unit 108 has a filtering processingsection 501, a hold time setting section 502, a sampling hold processingsection 503, another filtering processing section 504, a samplingprocessing section 505, a correlation value calculation section 506, anda deterioration degree calculation section 507.

The filtering processing section 501 filters the output voltage of thefront O₂ sensor 226. The filtering is performed by a weighted average orthe like.

The hold time setting section 502 map retrieves a hold time forcombining the output phases of the front O₂ sensor 226 and the rear O₂sensor 227 according to the engine speed and the intake pipe pressure.

The sampling hold processing section 503 samples the output of the frontO₂ sensor filtered by the filtering processing section 501 and processesto combine the phases of the output of the front O₂ sensor 226 and theoutput of the rear O₂ sensor 227 according to the hold time determinedby the hold time setting section 502.

The filtering processing section 504 filters the output voltage of therear O₂ sensor 227. The filtering processing is performed by theweighted average or the like in the same manner as the filtering of theoutput voltage of the front O₂ sensor 226.

The sampling processing section 505 samples the output of the rear O₂sensor filtered by the filtering processing section 504.

The correlation value calculation section 506 calculates a correlationvalue C for every prescribed interval according to the sampled value ofthe front O₂ sensor 26 from the sampling hold processing section 503 andthe sampled value of the rear O₂ sensor 227 from the sampling processingsection 505.

The correlation value C is calculated by following equation (1):$\begin{matrix}{C = {\sum\limits_{i = 1}^{{NUMBER}\quad{OF}\quad{SAMPLES}}{( {{{Pre}\quad(i)} - {Pre}} )^{2} \cdot ( {{{Post}\quad(i)} - {Post}} )^{2}}}} & (1)\end{matrix}$

In the equation, “Pre” denotes a sampled value of the front O₂ sensor,and “Post” denotes a sampled value of the rear O₂ sensor.

The deterioration degree calculation section 507 determines adeterioration degree (deterioration judging value) D of the catalystfrom the correlation value C for every prescribed interval calculated bythe correlation value calculation section 506.

FIG. 5 shows an example of a relationship between the correlation valueC and the deterioration degree D outputted from the front and rear O₂sensors.

A line 601 indicates the middle value between the correlation value Cand the deterioration degree D. The correlation value C and thedeterioration degree D have a certain degree of width between lines 602and 603 depending on individual variations with the line 601 at thecenter.

The threshold value becomes a line 604 when the deterioration degree Dis ineffective under emission control regulation I, and the thresholdvalue of the correlation value C judging that the catalyst deteriorationis ineffective becomes a threshold value 606 under the emission controlregulation I considering a width 605 of variation 1. Meanwhile, thethreshold value under another emission control regulation II becomes aline 607 when the deterioration degree D is ineffective, and thethreshold value of the correlation value D for judging the catalystdeterioration as ineffective can not be set considering a width 608 ofvariation 2.

FIG. 6A, FIG. 6B, FIG. 6C show one example of output behaviors of thefront and rear O₂ sensors in a case where a general example of catalystis judged as catalyst ineffective.

As shown in FIG. 6A, a front O₂ sensor 702 and a rear O₂ sensor 703 aredisposed before and after an ordinary catalyst 701 of a single bay.

A chart 704 of FIG. 6B shows the output of the front O₂ sensor 702,indicating that it is fluctuated with a prescribed voltage at the centerby the air/fuel ratio feedback control of the engine control unit.

Meanwhile, the catalyst 701 is deteriorated considerably to anineffective level in view of the emission control regulation but is notdeteriorated so much as a whole. Therefore, the output of the rear O₂sensor 703 is not fluctuated so heavily as indicated by a chart 705 inFIG. 6C. Thus, a correlation value for judgment of the catalystdeterioration becomes a small value close to 0.

FIG. 7A, FIG. 7B, FIG. 7C, FIG. 7D show an example of output behaviorsof the front and rear O₂ sensors in a case where the catalyst of thisembodiment is to be judged as catalyst ineffective.

As shown in FIG. 7A, the catalytic converter apparatus of thisembodiment is splited into the front catalyst 223 and the rear catalyst224 which are housed within the single housing 222, and the rear O₂sensor 227 mounted in the intermediate space 225 which is definedbetween the front catalyst 223 and the rear catalyst 224. The front O₂sensor 226 is mounted on the upper stream side of the front catalyst223.

The output of the front O₂ sensor 226 is fluctuated with a prescribedvoltage at the center by the air/fuel ratio feedback control asindicated by a chart 806 in FIG. 7B.

Meanwhile, where the catalyst as a whole is deteriorated so that theemission level is not conforming to the emission control regulation, thedeterioration degree of the front catalyst 223 is larger than that ofthe rear catalyst 224, so that the fluctuation width of the rear O₂sensor 227 mounted in the intermediate space 225 becomes large incomparison with the above case of the mounting position 703 shown inFIG. 6A as indicated by the chart 705 in FIG. 6C. Thus, a correlationvalue for judgment of the catalyst deterioration indicates a large valueto some extent.

FIG. 8 shows an example of a relationship between the correlation valueC and the deterioration degree D of the outputs of the front and rear O₂sensors.

By configuring the catalyst and the front and rear O₂ sensors as shownin FIG. 7A, the threshold value of a deterioration degree, which becomesan ineffective level under the emission control regulation, can beshifted from a region 905 to a region 907, and it is easy to determinethe threshold value of the correlation value.

In other words, the separation into the front catalyst 223 and the rearcatalyst 224 causes that the front catalyst 223 is deteriorated earlierthan when it is not separated, and it becomes possible to detect whetherthe catalyst is ineffective even if deterioration as a whole is little.

FIG. 9 shows an example of a relationship between the front catalystdeterioration degree and the rear catalyst deterioration degree in thecatalytic converter apparatus of this embodiment (the present invention)shown in FIG. 7A.

A line 1001 indicates a correlation value of the outputs of the frontand rear O₂ sensors to show a deterioration degree of the front catalyst223. If the line reaches a threshold value 1002 where it is judged asineffective, the failure diagnosis display unit 261 shows a screen forurging to replace. Then, the front catalyst 223 is replaced, and thedeterioration degree of the front catalyst 223 returns to zero as aresult of the replacement.

Meanwhile, the rear catalyst 224 is deteriorated slowly as indicated bya line 1005, and according to this embodiment, a deterioration degree ofthe rear catalyst 224 reaches an ineffective level 1006 at a point 1007for the meantime the front catalyst 223 was replaced two times.

The deterioration property of the rear catalyst 224 varies depending onthe distance between the front catalyst 223 and the rear catalyst 224,the space volume of the intermediate space 225 and the like, and thedeterioration degree of the front catalyst 223 may be used when the rearcatalyst 224 of a real automobile is judged as deteriorated.

In this embodiment, the deterioration degree of the rear catalyst 224has the integrated value of the front catalyst deterioration degreedetermined as a rear catalyst deterioration index based on therelationship between the front catalyst deterioration degree and therear catalyst deterioration degree shown in FIG. 9, andineffective/effective of the rear catalyst is determined according tothe rear catalyst deterioration index.

FIG. 10 shows an example of a relationship between the front catalystdeterioration degree and the front catalyst deterioration degreeintegrated value (rear catalyst deterioration index).

When a deterioration degree 1101 of the front catalyst 223 reaches athreshold value 1102, the catalyst is replaced with new one, and thedeterioration degree returns to zero. The ineffective level of the rearcatalyst deterioration of FIG. 9 described above is at 1103, and whenthe front catalyst deterioration degree integrated value 1101 reaches athreshold value 1105 corresponding to that level, the rear catalyst 224is judged as ineffective, and the failure diagnosis display unit 261urges the user or driver to replace the catalyst.

After the rear catalyst 224 is replaced, the front catalystdeterioration degree integrated value is cleared, and accumulation isrestarted. Upon reaching the threshold value 1105 again, the failurediagnosis display unit 261 urges the user to replace the rear catalyst224.

FIG. 11 shows an example of separation of a catalyst of the catalyticconverter apparatus of this embodiment. Both the front catalyst 223 andthe rear catalyst 224 have a columnar shape. The axial length of thefront catalyst 223 is L1, and the axial length of the rear catalyst 224is L2 which is longer than the axial length L1 of the front catalyst223. Because of the difference in the axial length, the volume of thefront catalyst 223 is smaller than that of the rear catalyst 224. Theintermediate space 225 having an axial length L3 is present between thefront catalyst 223 and the rear catalyst 224.

A relationship of the front catalyst 223 to the deterioration propertydue to a combination of the front catalyst 223 and the rear catalyst 224is derived.

It is assumed that an HC (hydrocarbon) transformation efficiency isEfnew when the catalyst is new and an HC transformation efficiency isEfng when the catalyst is ineffective. Then, a split ratio L1:L2 of thefront catalyst 223 and the rear catalyst 224 is expressed by followingequation (2). The HC transformation efficiency here indicates atransformation efficiency of the combination of the front catalyst 223and rear catalyst 224.L1:L2={(Efnew-Efng)/Efnew}:(Efng/Efnew)  (2)

When it is assumed that Efnew=90% and Efng=70%, it becomes thatL1:L2=22%:78%, and a split ratio with allowance included becomesL1:L2=30%:70%.

Thus, the catalytic converter apparatus is separated into the frontcatalyst 223 and the rear catalyst 224 at a prescribed split ratioaccording to the transformation efficiency when they are new, thetransformation efficiency when ineffective and the emission measuredvalue. The volume of the front catalyst 223 is smaller than that of therear catalyst 224.

The deterioration of the rear catalyst 224 becomes slower in comparisonwith the deterioration of the front catalyst 223 as the intermediatespace 225 has a larger volume. Therefore, the relationship between thefront catalyst deterioration degree and the rear catalyst deteriorationdegree shown in FIG. 9 is determined considering the volume of theintermediate space 225.

In other words, where the relationship of the front catalyst 223 to thedeterioration property according to the combination of the frontcatalyst 223 and the rear catalyst 224 is derived, the volume of theintermediate space 225 is added to the elements contributing to thedeterioration of the rear catalyst 224.

FIG. 12 shows an example of one structure of an effective/ineffectivejudgment processing section (apparatus for diagnosing deterioration of acatalyst) of the front catalyst 223 and the rear catalyst 224.

The effective/ineffective judgment processing section of this embodimenthas a front catalyst deterioration judging value calculation section1401, a front catalyst effective/ineffective judging section 1402, afront catalyst ineffective-to-effective invert times counter 1405, anineffective-to-effective invert times threshold value setting device1406, a comparator 1407, a rear catalyst effective/ineffective judgingsection 1409, a front catalyst deterioration judging value integratingsection 1411, a front catalyst deterioration judgment integrated valuestorage section 1414, and switches 1408, 1412, 1413.

The front catalyst deterioration judging value calculation section 1401is configured of, for example, the front catalyst deterioration degreearithmetic processing section shown in FIG. 4, and the front O₂ sensoroutput, the rear O₂ sensor output, the intake pipe pressure and theengine speed are inputted, and then the deterioration judging value(deterioration degree) of the front catalyst is calculated by correlatedcalculation.

The front catalyst effective/ineffective judging section 1402 judgeseffective/ineffective of the front catalyst 223 according to the frontcatalyst deterioration judging value calculated by the front catalystdeterioration judging value calculation section 1401.

In a case where it is judged as ineffective by the front catalysteffective/ineffective judging section 1402, it is notified to the driverby the diagnosis display made by the failure diagnosis display unit 261,the code of the front catalyst ineffective is written into the storageunit 262, and the count value of the front catalystineffective-to-effective invert times of the front catalystineffective-to-effective invert times counter 1405 is increased by oneincrement.

The comparator 1407 compares the ineffective-to-effective invert timesthreshold value which is set in the ineffective-to-effective inverttimes threshold value setting device 1406 with the count value of thefront catalyst ineffective-to- effective invert times counter 1405. Inthis comparison, if the count value of invert times is larger than thethreshold value, the deterioration judging value of the front catalyst223 according to the front catalyst deterioration judging valuecalculation section 1401 is inputted to the rear catalysteffective/ineffective judging section 1409 by the switch 1408.

The front catalyst deterioration judging value integrating section 1411integrates the deterioration judging values (deterioration degrees) ofthe front catalyst 223 calculated by the front catalyst deteriorationjudging value calculation section 1401. This integration is continueduntil the switch 1413 is turned off after the rear catalyst 224 isjudged as ineffective by the rear catalyst effective/ineffective judgingsection 1409, and the integrated value at this point is written as thefront catalyst deterioration judgment integration stored value into thefront catalyst deterioration judgment integrated value storage section1414 via the switch 1412.

The rear catalyst effective/ineffective judging section 1409 judgeswhether the rear catalyst 224 is effective or ineffective according tothe deterioration judging value of the front catalyst 223 calculated bythe front catalyst deterioration judging value calculation section 1401or the front catalyst deterioration judgment integrated value integratedby the front catalyst deterioration judging value integrating section1411.

Where it is judged by the rear catalyst effective/ineffective judgingsection 1409 that the rear catalyst 224 is ineffective, it is notifiedto the driver by the diagnosis display made by the failure diagnosisdisplay unit 261, and a rear catalyst ineffective code is written intothe storage unit 263.

The storage units 262, 263 are the same storage unit except that thefront catalyst ineffective code and the rear catalyst ineffective codehave a different memory address.

FIG. 13 shows an example of another structure of theeffective/ineffective judgment processing section (apparatus fordiagnosing deterioration of a catalyst) of the front catalyst 223 andthe rear catalyst 224. In FIG. 13, portions corresponding to those ofFIG. 12 are denoted by like reference numerals as those used in FIG. 12,and descriptions thereof will be omitted.

This embodiment is different from that of FIG. 12 described above on thepoint that the embodiment of FIG. 12 counts the front catalystineffective-to-effective invert times, while this embodiment counts thenumber of replacement times of the front catalyst 223.

In this embodiment, a front catalyst replacement times counter 1505 forcounting the number of replacement times of the front catalyst 223, areplacement times threshold value setting device 1506, and a comparator1507 for comparing the replacement times threshold value set in thereplacement times threshold value setting device 1506 with the countvalue of the front catalyst replacement times counter 1505 are disposed,and the output of the comparator 1507 controls the switch 1408 in thesame manner as in the embodiment of FIG. 12 described above. The countvalue of the front catalyst replacement times counter 1505 is updated bya car repair shop or the like by manually inputting when the frontcatalyst 223 is replaced.

Details of the rear catalyst effective/ineffective judging section 1409will be described with reference to FIG. 14.

The rear catalyst effective/ineffective judging section 1409 has a rearcatalyst effective/ineffective judgment discrimination portion 1601, acomparator 1604, and switches 1602, 1603 for switching the input of thecomparator 1604.

The rear catalyst effective/ineffective judgment discrimination portion1601 judges whether or not the ineffective judgment of the rear catalyst224 was done in the past, and if the ineffective judgment was not madeat all, the front catalyst deterioration judging value (deteriorationdegree) is selected for the comparative value and the front catalystdeterioration judgment threshold value is selected for the thresholdvalue by the switches 1602, 1603 as inputs to the comparator 1604, andthey are compared by the comparator 1604 according to the structureshown in FIG. 12 or FIG. 13.

Where the front catalyst deterioration judging value inputted to thecomparator 1604 is larger than the front catalyst deterioration judgmentthreshold value, the rear catalyst 224 is judged as ineffective.

Meanwhile, if it was judged as ineffective even once in the past, thefront catalyst deterioration judgment integrated value and the frontcatalyst deterioration judgment integration stored value as a thresholdvalue are selected as inputs to the comparator 1604 by the switches1602, 1603, and they are compared by the comparator 1604.

Where the front catalyst deterioration judgment integrated value to beinputted to the comparator 1604 is larger than the front catalystdeterioration judgment integration stored value, the rear catalyst isjudged as ineffective.

A processing flow of overall control to be performed by the enginecontrol unit 250 including the catalyst deterioration judgment of thisembodiment will be described with reference to the flowchart of FIG. 15.

First, the electrical signals of the crank angle sensor 213, and mainlythe number of inputs per unit time of a change in pulse signal arecounted, and the engine speed is calculated by arithmetic processing instep 1701. In step 1702, the intake pipe pressure is read by the outputfrom the intake pipe pressure sensor 205.

Subsequently, a basic amount of fuel is calculated based on the enginespeed and the intake pipe pressure in step 1703.

Then, a basic fuel correction factor is retrieved based on the enginespeed and the intake pipe pressure in step 1704.

The output of the front O₂ sensor 226 which is in front of the catalystis read in step 1705.

Air/fuel ratio feedback control is performed based on the output signalof the front O₂ sensor 226 to obtain a target air/fuel ratio in step1706, thereby determining an air/fuel ratio feedback controlcoefficient.

The output of the rear O₂ sensor 227 which is after the catalyst is readin step 1707.

Then, a deterioration degree (deterioration judging value) of the frontcatalyst 223 is calculated by correlated calculation according to thefront O₂ sensor output and the rear O₂ sensor output in step 1708.

A deterioration degree of the rear catalyst 224 is calculated based onthe deterioration degree of the front catalyst 223 described above instep 1709.

The basic amount of fuel is corrected according to the basic fuelcorrection factor and the air/fuel ratio feedback control coefficient instep 1710. And, an amount of fuel to inject the corrected amount of fuelis set in step 1711.

Then, a target engine speed for idling is calculated in step 1712. And,a target flow rate of the ISC valve 203 is calculated from the targetengine speed in step 1713.

An ignition timing compensation amount for suppressing the idling speedfrom varying is calculated in step 1714.

The target flow rate of the ISC valve 203 is outputted to the ISC valve203 to control the ISC valve 203 in step 1715.

Then, a throttle opening degree is read in step 1716. And, a time changeamount of the read throttle opening degree is determined to judgeacceleration or deceleration in step 1717.

An ignition timing compensation amount for acceleration or decelerationis calculated based on the acceleration or deceleration judgment in step1718.

A basic ignition timing is calculated in step 1719. And, the calculatedignition timing compensation for idling, acceleration or deceleration isapplied to the basic ignition timing in step 1720 to determine the finalignition timing. And, the final ignition timing is set in step 1721, andignition is performed at the required ignition timing.

Then, a processing flow of the catalyst deterioration degree calculationof the front catalyst by the front catalyst deterioration degreearithmetic processing section shown in FIG. 4 will be described withreference to the flowchart of FIG. 16.

First, the output of the front O₂ sensor 226 is read in step 1801. And,the output of the front O₂ sensor 226 is filtered in step 1802.

An engine speed and an intake pipe pressure are read in step 1803, and ahold time for combining the phases of the outputs of the O₂ sensorsbefore and after the catalyst according to the engine speed and theintake pipe pressure is map retrieved in step 1804. The filtering valueof the front O₂ sensor 226 is sampled while reflecting the hold time instep 1805.

The output of the rear O₂ sensor 227 is read in step 1806. And, theoutput of the rear O₂ sensor 227 is filtered in step 1807. The filteringvalue of the rear O₂ sensor 227 is sampled in step 1808.

A correlation value of a prescribed interval is calculated from thesample values of the filtering values of the O₂ sensors before and afterthe catalyst in step 1809. The correlation value is calculated by theabove-described equation (1).

The deterioration judging value (deterioration degree) of the frontcatalyst 226 is determined from the correlation value in step 1810.

The processing flow of the effective/ineffective judgment of the frontcatalyst 223 and the rear catalyst 224 by the effective/ineffectivejudgment processing section shown in FIG. 12 will be described withreference to the flowchart of FIG. 17.

The outputs of the O₂ sensors 226, 227 before and after the catalyst areread in step 1901. And, the engine speed and the intake pipe pressureare read in step 1902.

The deterioration judging value of the front catalyst 226 is calculatedfrom the outputs of the O₂ sensors before and after the catalyst, theengine speed and the intake pipe pressure in step 1903. Thisdeterioration judging value is calculated from the correlation value ofthe outputs of the front and rear O₂ sensors according to the processingflow shown in FIG. 16.

Then, the deterioration of the front catalyst 223 is judged foreffective/ineffective according to the deterioration judging value instep 1904.

The procedure is branched in step 1905 depending on the judged resulteffective or ineffective determined in step 1904. If the judged resultis ineffective, the procedure advances to step 1907, where ineffectivecode 1 of the front catalyst ineffective is stored, and a failurewarning is given by the failure display unit 261 in the next step 1908.

If the judged result of the front catalyst 223 is effective, theprocedure advances to step 1906, and the failure warning is cancelled.

It is judged in step 1909 whether there is an integration stored valueof the deterioration judging value of the front catalyst 223. If thereis not an integration stored value, the procedure advances to step 1910,where it is judged whether the deterioration judgment of the frontcatalyst 223 is inverted from ineffective to effective.

If it is inverted, the procedure advances to step 1911, where the numberof ineffective-to-effective invert times is counted to judge whether thenumber of invert times is equal to or more than the threshold value instep 1912. If the number of invert times is equal to or more than thethreshold value, the procedure advances to step 1913, where thedeterioration judging value of the front catalyst 223 is read. And, thedeterioration judgment of the rear catalyst 224 is judged foreffective/ineffective from the deterioration judging value of the frontcatalyst 223 in step 1914.

The procedure is branched in step 1915 depending on the judged resulteffective or ineffective in step 1914. If the judged result isineffective, the procedure advances to step 1917, where ineffective code2 of the rear catalyst ineffective is stored, and a failure warning isgiven by the failure display unit 261 in the nest step 1918.

If the judged result of the rear catalyst 224 is effective, theprocedure advances to step 1916, where the failure warning is cancelled.

If it is judged in the step 1909 that there is a deterioration judgmentintegration stored value of the front catalyst 223, the procedureadvances to step 1919, where the deterioration judgment integrationstored value and the front catalyst deterioration judgment integratedvalue (threshold value) are compared to judge whether the rear catalyst224 is effective or ineffective.

If the front catalyst deterioration judgment integrated value is largerthan the deterioration judgment integration stored value, the rearcatalyst is ineffective. Then, the code 2 of the rear catalystineffective is stored and a failure warning is given in steps 1917,1918. Meanwhile, if the front catalyst deterioration judgment integratedvalue is not larger than the deterioration judgment integration storedvalue, the procedure advances to step 1916, where the failure warning iscancelled.

FIG. 18 shows a processing flow of the front catalyst deteriorationjudging value integration and judging value storing performed by theineffective judgment processing section shown in FIG. 12.

The front catalyst deterioration judging value is read in step 2001. Thefront catalyst deterioration judging value is integrated in step 2002.

It is judged in step 2003 whether the rear catalyst 224 is judged asineffective. If the rear catalyst 224 is judged as ineffective, theprocedure advances to step 2004, where the above-described integratedvalue is stored, and the integration is stopped in step 2005.

Then, the processing flow of effective/ineffective judgment by theeffective/ineffective judgment processing section of the front catalyst223 and the rear catalyst 224 shown in FIG. 13 will be described withreference to the flowchart of FIG. 19. In FIG. 19, steps correspondingto those of FIG. 17 are denoted by the same step numbers as those usedin FIG. 17, and descriptions thereof will be omitted.

In this processing flow, it is judged in step 2110 whether or not thefront catalyst replacement signal to be manually inputted is present,and a replacement times count value is incremented in step 2111. And, itis judged in step 2112 whether the count value is equal to or more thana threshold value, and it is judged whether the deterioration of therear catalyst 224 is effective or ineffective.

Excepting the above, it is configured such that the processing flow isthe same as in the flowchart shown in FIG. 17.

Then, the processing flow of the rear catalyst effective/ineffectivejudgment by the rear catalyst effective/ineffective judging section 1409shown in FIG. 14 will be described with reference to the flowchart ofFIG. 20.

It is judged in step 2201 whether the deterioration ineffective of therear catalyst 224 has been judged. If the ineffective judgment has notbeen made, the procedure advances to step 2202, where the front catalystdeterioration judging value is selected as a comparative value, and thefront catalyst deterioration judgment threshold value is selected as athreshold value in step 2203.

Meanwhile, if it was judged as ineffective, the procedure advances tostep 2204, where the front catalyst deterioration judgment integratedvalue is selected as a comparative value, and the front catalystdeterioration judgment integration stored value is selected as athreshold value in step 2205.

It is judged in step 2206 whether the comparative value is equal to ormore than the threshold value, and if the comparative value is equal toor more than the threshold value, it is judged in step 2207 that therear catalyst 224 is ineffective, and if the comparative value is notequal to or more than the threshold value, it is judged in step 2208that the rear catalyst is effective.

As described above, the catalytic converter apparatus is separated intothe front catalyst 223 and the rear catalyst 224 at a prescribed splitratio according to a transformation efficiency when they are new, atransformation efficiency when ineffective and an emission measuredvalue, and the O₂ sensors 226, 227 are mounted before the separatedfront catalyst 223 and at the split point between them. And, thedeterioration of the catalyst is diagnosed by comparing the outputs ofthe front and rear O₂ sensors, so that the front catalyst isdeteriorated earlier than when it is not separated, and it becomespossible to detect ineffective even if the deterioration is slight as awhole. And, the deterioration degree of the rear catalyst 224 isobtained according to the deterioration degree and the number ofreplacement times of the front catalyst 223, so that the front catalyst223 is not replaced even if it is deteriorated.

The front catalyst 223 and the rear catalyst 224 are housed in thesingle housing 222 in the embodiment described above, but the apparatusof the invention is not limited to it. As shown in FIG. 21, the frontcatalyst 223 and the rear catalyst 224 may be housed in separatehousings 222A, 222B. In FIG. 21, portions corresponding to those of FIG.1 are denoted by like reference numerals as those used in FIG. 1, anddescriptions thereof will be omitted.

Instead of the O₂ sensors 226, 227, a sensor which outputs a signalcorresponding to the oxygen density or fuel concentration contained inthe exhaust gas can also be used.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. An apparatus for diagnosing deterioration of a catalyst for aninternal combustion engine, having a first catalyst and a secondcatalyst and provided with sensors for detecting a particular exhaustcomponent before and after the first catalyst, wherein: a relationshipbetween a deterioration property involved in clarification of an exhaustgas of the internal combustion engine by a combination of the firstcatalyst and the second catalyst and a deterioration property of thefirst catalyst are determined previously; a deterioration degree of thefirst catalyst is calculated according to outputs from the sensorsdisposed before and after the first catalyst; deterioration of the firstcatalyst is judged according to the deterioration degree; anddeterioration of the second catalyst is judged according to thedeterioration degree of the first catalyst.
 2. The apparatus fordiagnosing deterioration of a catalyst for an internal combustion engineaccording to claim 1, wherein a volume of a space between the firstcatalyst and the second catalyst is added to elements contributing tothe deterioration of the second catalyst when a relationship of thefirst catalyst to the deterioration property due to the combination ofthe first catalyst and the second catalyst is derived.
 3. The apparatusfor diagnosing deterioration of a catalyst for an internal combustionengine according to claim 1, wherein the sensors for detecting theparticular exhaust component are O₂ sensors which output a binary outputfor the presence or not of oxygen contained in the exhaust gas.
 4. Theapparatus for diagnosing deterioration of a catalyst for an internalcombustion engine according to claim 2, wherein the sensors fordetecting the particular exhaust component are O₂ sensors which output abinary output for the presence or not of oxygen contained in the exhaustgas.
 5. The apparatus for diagnosing deterioration of a catalyst for aninternal combustion engine according to claim 1, wherein the sensors fordetecting the particular exhaust component are sensors which output asignal corresponding to an oxygen density or a fuel concentrationcontained in the exhaust gas.
 6. The apparatus for diagnosingdeterioration of a catalyst for an internal combustion engine accordingto claim 2, wherein the sensors for detecting the particular exhaustcomponent are sensors which output a signal corresponding to an oxygendensity or a fuel concentration contained in the exhaust gas.
 7. Amethod for diagnosing deterioration of a catalyst for an internalcombustion engine, having a first catalyst and a second catalyst andprovided with sensors for detecting a particular exhaust componentbefore and after the first catalyst, comprising: determining previouslya relationship between a deterioration property involved inclarification of an exhaust gas from the internal combustion engine by acombination of the first catalyst and the second catalyst and adeterioration property of the first catalyst; calculating adeterioration degree of the first catalyst according to outputs from thesensors disposed before and after the first catalyst; judgingdeterioration of the first catalyst according to the deteriorationdegree; and judging deterioration of the second catalyst according tothe deterioration degree of the first catalyst.
 8. A catalytic converterapparatus for exhaust emission disposed in an exhaust gas passage of aninternal combustion engine, the apparatus having a first catalyst and asecond catalyst, and a volume of the first catalyst disposed on theupper stream side of an exhaust gas flow in the exhaust gas passage issmaller than that of the second catalyst disposed on the down streamside.
 9. The catalytic converter apparatus according to claim 8, whereina proportion of a volume of the first catalyst to that of the secondcatalyst is determined to be smaller according to a proportion of anunburnt gas conversion efficiency of a combination of the first catalystand the second catalyst when they are new to an unburnt gas conversionefficiency at the time when an emission level is judged as ineffective.10. The catalytic converter apparatus according to claim 8, wherein thefirst catalyst and the second catalyst are stored in one and the samehousing.
 11. The catalytic converter apparatus according to claim 9,wherein the first catalyst and the second catalyst are stored in one andthe same housing.